Rheological and Rheo-Optical Investigation of Cellulose Ethers in Aqueous Solution

The opportunities provided by rheo-optical techniques for the investigation of cellulose derivatives in solution are discussed. Flow birefringence experiments yield information on the optical properties of the material and allow to distinguish between the contribution of different structural elements like, for example, the dangling chains and the anisotropic stem of fringed micelles on shear thinning and flow orientation, respectively. Rheo-turbidity and rheo-small angle light scattering measurements were used to study the influence of shear on the phase separation that occurs in aqueous methyl hydroxypropyl cellulose (MHPC) solutions upon heating. Both shear induced mixing and demixing were found and also differences between temperature ramp and shear rate ramp experiments were observed. The differences between chemical and physical crosslinking of MHPC were characterized by low amplitude oscillatory shear measurements. Finally, the possibility to prepare microgels by shearing the samples during the crosslinking reaction is reported.